1. Field of Invention
This invention relates generally to bearing assemblies for supporting rotatable shafts or posts, and more particularly to a ball and socket bearing assembly adapted to align itself with a vertical rudder post extending therethrough regardless of the degree to which the post deviates from the vertical as a result of hydrodynamic or other forces imposed on the rudder.
2. Status of the Prior Art
A sailboat or a power boat is steered by a rudder in the form of a flat surfaced structure or blade hinged to the stern of the vessel and controlled by a helm. When the boat advances in a straight course, the rudder is then in line with the boat. But if the rudder is turned by the helm to one side or the other, it offers sufficient resistance to the water impinging on its surface to deflect the stern and thereby change the direction in which the boat advances.
In a typical sail or power boat installation, the rudder which is below the hull is joined to a rudder post which passes through a bronze or brass sleeve fastened to the hull, the post terminating in a lever or steering arm functioning as the helm. The metal sleeve is sealed by a packing gland affixed thereto to prevent water from entering the boat. To maintain the rudder post in its proper upright position, a bearing assembly is provided that is supported on a horizontal plate or platform cantilevered from the stern at a position below the steering arm, the rudder post passing through this assembly. The bearing assembly is adapted to sustain the side loads to which the post is subjected as well as to prevent the rudder post from slipping down into the water.
In operation, exerted on the rudder are hydrodynamic forces whose direction depend on the orientation of the rudder relative to the water stream impinging on its surface. These forces which are transmitted to the rudder post seek to laterally displace the post. The function of the bearing assembly through which the post passes is to resist these forces which are sometimes considerable, and thereby maintain the rudder post at its proper position.
A similar problem arises in propeller-driven vessels in which the rotating shaft turning the propeller may not be accurately aligned, and thereby requires a bearing assembly that will align itself with the shaft regardless of the degree to which its axis of rotation deviates from a nominal axis. Thus the Robbins U.S. Pat. No. 1,063,389, and the Schmitt U.S. Pat. No. 1,024,884 show self-aligning ball and socket bearing arrangements for motor boat propeller shafts which allow freedom of movement to the shaft in the absence of true shaft alignment.
Of greatest prior art interest is the Strong et al. U.S. Pat. No. 5,346,315. This patent discloses a ball and socket assembly adapted to engage the post of a rudder installed in the stern of a boat and to maintain it at a proper upright position regardless of the degree to which the post deviates from the vertical and is subjected to hydrodynamic forces which seek to displace the post.
The assembly consists of a journal box fixedly mounted on a support and having a spheroidal cavity, and a bearing through which the rudder post extends which is formed of UHHW polyethylene. The bearing includes a spheroidal or bulbous section that nests within the cavity of the box and a cylindrical section projecting from the box and pinned to the post whereby the bearing is in alignment with the post and its spheroidal section, is free to rotate within the cavity of the journal box in accordance with the rotation of the post as the boat is steered.
One practical drawback to a ball and socket assembly of the type disclosed in the prior Strong et al. patent is that it is relatively expensive to fabricate. The reason for this is that the journal box consists of two plastic plates formed of the same UHMW polyethylene material as the bearing, the plastic plates having contoured openings machined therein so that when put in superposed relation, they then define the spheroidal cavity in which the bearing is nested.
To put together the prior Strong et al. ball and socket bearing assembly, one must place the lower portion of the bulbous section of the UHMW bearing within the contoured opening of the lower plate, and then place the upper plate over the lower plate so that the upper portion of the bearing lies with the contoured opening of the upper plate. The superposed plastic plates are then riveted together to lock the bearing therein.
The manufacture of this assembly is time consuming and costly, requiring separate machining of the two plates forming the journal box, for the shape of the cavity in the journal box must properly match the shape of the bearing nested therein.